<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        html,body{
            height: 100%;
            width: 100%;
        }
        .nav{
            background-color: red;
            color:white;
            width: 100%;
            height: 50px;
            text-align: center;
            margin: 0 auto;
        }
        .parent{
            color:white;
            height: calc(100% - 50px);
            display: flex;
            justify-content: space-around;
            align-items: center;
        }
        .one{
            width:25%;
            height: 100%;
            background-color:green;
        }
        .two{
            width: 50%;
            height: 100%;
            background-color: gray;
        }
        .three{
            width: 25%;
            height: 100%;
            background-color: green;
        }
    </style>
    <div class="nav">我是导航栏</div>
    <div class="parent">
        <div class="one">我是左边框</div>
        <div class="two">我是内容区</div>
        <div class="three">我是右边框</div>
    </div>
</body>
</html>